This invention relates to methods and arrangements for installing and removing rotors in permanent magnet machines.
Installation and removal of rotor assemblies containing energized permanent magnets in the stators of large sized permanent magnet machines requires special and quite expensive fixtures in order to properly guide and hold the rotor assembly centered while the rotor is being inserted within the stator assembly. This is necessary to prevent the rotor from being drawn by the energized permanent magnets laterally toward the stator assembly during insertion and removal because the energized permanent magnets generate high magnetic fields producing attraction and/or repulsion forces.
For small or medium sized permanent magnet machines the rotor can contain magnets which are not energized until after the assembly has been completed if the core stack length and the number of magnets per pole are amenable to magnet energization following assembly. This is normally not practical, however, for large permanent magnet machines and, for such machines, the fixtures required for mounting a rotor containing energized permanent magnets in a stator are generally unique to a particular machine design, are expensive, and must accompany the machine for field disassembly since rotor removal requires the use of the same fixtures as for the assembly process. If a problem such as a winding short occurs in a permanent magnet machine or if periodic maintenance is required the machine must typically be partially or fully disassembled using the unique fixture.
The Keim et al. U.S. Pat. No. 5,831,365 discloses a detachable magnet carrier for a permanent magnet rotor in which a magnet carrier containing a linear array of permanent magnets can be pushed into a groove in a rotor after the rotor has been installed in a permanent magnet machine and attached to the rotor structure by screws.
The Adelski et al. U.S. Pat. No. 4,439,704 discloses a method for manufacturing a rotor in which individual permanent magnets are inserted in succession into a slot extending through the rotor laminations from one end to the other of the rotor until the slot has been filled and the opposite ends of the rotor are covered by shorting ring segments so that each row of magnets is covered at one end by a shorting ring segment.
U.S. Pat. No. 6,047,461 to Miura et al. discloses the manufacture of a permanent magnet rotor in which dummy magnet pieces are used to facilitate the fitting of a steel sleeve over permanent magnets and are then removed after assembly of the rotor.
Accordingly, it is an object of the present invention to provide a method and arrangement for installation and removal of energized permanent magnets in permanent magnet rotors which overcomes disadvantages of the prior art.
Another object of the present invention is to provide a method and arrangement for installation and removal of energized permanent magnets in permanent magnet rotors in a simple and relatively inexpensive manner.
These and other objects of the invention are attained by mounting a rotor containing nonmagnetic dummy magnet blocks into a stator assembly and then replacing the nonmagnetic dummy magnet blocks with energized permanent magnets. Preferably the nonmagnetic dummy blocks are slidably supported in a passage extending parallel to the axis of the rotor and a loading fixture containing permanent magnets is aligned with the passage containing the dummy magnet blocks. The permanent magnets are then pushed into the passage and the dummy magnet blocks are removed from the opposite end of the passage.
Installation of permanent magnets in this manner is carried out in succession in each magnet row of the rotor until all of the dummy magnet blocks have been completely replaced by permanent magnets, after which the passages are closed at each end, for example by mounting end plates at the ends of the passages in the rotor assembly to retain the permanent magnets in position in the rotor. Thus, by first mounting a rotor with dummy magnet blocks in passages in the rotor of a permanent magnet machine, then installing the rotor in the stator of the machine, and then replacing the dummy blocks with permanent magnets while removing the dummy magnet blocks, the necessity for using complex and expensive rotor positioning fixtures for installing the rotor is avoided. Moreover, if it is necessary to remove and replace permanent magnets in the rotor such replacement can be accomplished without disassembly of the permanent magnet machine.